Practical silicon photonic multi-function integrated-optic chip for fiber sensor applications

ABSTRACT

This patent disclosure is based on a silicon, instead of LiNbO 3 , waveguide chip. The disclosed silicon-based multi-function integrated-optic chip comprises a unique design and fabrication features onto it. A unique polarization-diversity coupler is designed and fabricated to couple the external light into the silicon waveguide structure. A unique two-step (vertical and lateral) taper waveguide region is designed and fabricated to bridge the polarization-diversity coupler output with the input of a multi-mode interferometer (MMI) splitter for power loss reduction. At either end of the Y-junction output, there is a phase modulator to achieve optical phase modulation through various physics mechanisms. With this newly-developed silicon-based multi-function integrated optic chip, the size and cost of fiber sensors including FOG&#39;s can be greatly reduced.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/191,954, which was filed Jul. 27, 2011, and is incorporated herein byreference as if fully set forth.

FIELD OF THE INVENTION

The invention relates to an optical chip, more particularly thisinvention is a silicon-based Multi-function Integrated-Optic Chip (MIOC)incorporates a unique polarization diversity coupler, and the two-steptaper waveguide designs for single polarization, and low loss sensorapplications. The silicon based waveguide is compatible with CMOS(Complementary Metal-Oxide Semiconductor) fabrication process, sointegration of optical waveguide with electronic circuit in one chip isfeasible that the size and cost of fiber sensors including Fiber-OpticGyroscopes (FOG's) can be greatly reduced.

BACKGROUND OF THE INVENTION

Microminiaturization plays an increasingly imperative role in our dailylife, especially for applications such as positioning, navigation andattitude control. Therefore, there is a need to develop highlyintegrated, sensitive and miniaturized gyroscopes to be incorporated asrotation sensors for the above mentioned applications.

Among all kinds of approaches in the prior art, FOG's based on Sagnaceffect (R. A. Bergh, H. C. Lefevre, H. J. Shaw, “An Overview ofFiber-Optic Gyroscopes”, J. Lightwave Technol., vol. 2, n.2, pp. 91-107,February 1984 and M. N. Armenise, C. Ciminelli, F. De Leonardis, R.Diana, F. Peluso, V. M. N. Passaro, “Micro Gyroscope Technologies forSpace Applications”, Internal Report, ESA-ESTEC Iolg Project, ContractDEE-MI, May 2003) are extensively used. One of the key components insidea FOG is the photonic chip mastering optical signal processing (M. N.Armenise, V. M. N. Passaro, F. De Leonardis, M. Armenise, “Modeling andDesign of a Novel Miniaturized Integrated Optical Sensor for GyroscopeApplications”, J. Lightwave Technology, vol. 19, n. 10, pp. 1476-1494,2001. 1).

Prior to the present invention, the traditional fiber sensors such asFOG's employing LiNbO₃ as the waveguide material for MIOC had beenreported (U.S. Pat. No. 5,223,911). The LiNbO₃-based fabricationprocesses result in a relatively larger and more expensive chip due tosmooth waveguide bending requirement, and is not compatible with themainstream integrated circuit processes.

Other than LiNbO₃ MIOC, silicon-based MIOC had also been reportedpreviously (U.S. Pat. No. 5,154,917, and patent application Ser. No.11/497,020). Comparing to other types of integrated optic waveguides,cost of a silicon-based optical waveguide is relatively low becausethere is plenty of supply for silicon. Also, within the large operatingtemperature range, silicon chemical property is benign and stable. Nochemical reaction is anticipated. Besides, silicon-based opticalwaveguides allow large angle splitting and even a 90 degree waveguidebend which greatly reduce the optic chip length from centimeter tomillimeter scale, and hence cut down the optic chip cost and sensordimension. Above all, the silicon waveguide is compatible with CMOSfabrication process, so integration of optical waveguide with electroniccircuit in one optic chip is feasible.

However, so far there is no commercially available FOG's claimed onsilicon-based MIOC technology due to design deficiencies or processcomplications. Examples such as for single mode, single polarizationoperations for sensor applications, U.S. Pat. No. 5,154,917 didn'taddress the polarizer issue, and Ser. No. 11/497,020 employed astandalone polarizer which inherently increasing the chip length and itsassociated optical loss.

According to the present invention, applicants have departed from theconventional wisdom, and had conceived and implemented a practicalsilicon-based MIOC to integrate functions of Y-junction splitter,polarizer, and phase modulators on the single optical chip through theimplementation of a unique polarization diversity coupler which iscapable of separating TE and TM modes in less than 100 μm length, andthe two-step taper waveguide designs for single-mode, and low losssensor applications such as for miniaturized FOG's. Such integration hasadditional advantages in reducing the cost of individual componentpackage and perhaps, the effort of alignment. Moreover, through matureIC fabrication technology, the production cost could decrease and thedevice performance improves. The invention is briefly described asfollows.

SUMMARY OF THE INVENTION

Unlike other materials such as silica and lithium niobate, silicon canbe utilized to make highly-confined waveguide (silicon photonics wires),dramatically reducing the footprint of the device. Potentially, siliconphotonics can monolithically integrate signal-processing circuits on asingle chip. In the present invention, we focus on developing aminiaturized fiber optical gyroscope employing a silicon-based MIOC withthe features of single-mode, single polarization operation, and smallsize, low loss and high bandwidth phase modulation. The basic idea is tointegrate all optical components, especially the unique polarizationdiversity coupler and the two-step taper waveguides, on a single siliconchip based on CMOS processes. Trough mature IC fabrication technology,the production cost could decrease and the device performance improves.

The present invention provides an optic chip and fabrication methodthereof. The silicon-based integrated photonics chip of the presentinvention comprises at least a polarization diversity coupler which isdesigned based on the asymmetry in index of optical refraction. Awaveguide is included in the present polarization diversity couplerwhich can divide an external electromagnetic wave into two components:TE and TM waves, and make one of the TE and TM electromagnetic wave becoupled into the waveguide.

In accordance with one aspect of the present invention, an optic chip isprovided. The optic chip includes a two-step taper waveguide bridged thewaveguide and a multi-mode interferometer (MMI) splitter. When thepolarized electromagnetic wave from the waveguide propagates to the MMI,it can reduce an optical loss and realizes a single-mode propagation.

In accordance with further aspect of the present invention, an opticchip is provided. The optic chip includes a multi-mode interferometer(MMI) splitter connected to the two-step waveguide and the phasemodulator. The MMI has a first plurality of waveguides at the input endand a second plurality of waveguides at the output end. Eitherwaveguides connected to the output ends of MMI can modulate the phase ofthe electromagnetic wave by controlling the concentration of its freecarriers.

From the above descriptions, the present invention also discloses amethod for manufacturing an optic chip, including the following steps:(1) a bottom clad layer on a substrate is provided, (2) a polarizationdiversity coupler having a waveguide and a top clad layer is formed onthe bottom clad layer, wherein the polarization diversity coupler isdesigned according to a first pattern and generates a TE and TMelectromagnetic wave from an external electromagnetic wave based on thethickness of the waveguide and the top clad layer, one of the TE and TMelectromagnetic waves is coupled into the waveguide while achievingphase matching between the polarized electromagnetic waves, and one ofwhich travels through the waveguide and the other travels through thetop clad layer, (3) a two-step taper waveguide is connected with the apolarization diversity coupler, wherein the two-step taper waveguide isdesigned according to a second pattern, in order to reduce optical lossand remain the single-mode propagation, and (4) a multi-modeinterferometer (MMI) is connected with the two-step taper waveguideoutput, wherein the MMI having a plurality of waveguides at the outputand input end is designed according to a third pattern, in order torealize a single-mode propagation.

The present invention provides an optic component and fabrication methodthereof. The optic component has a waveguide, being covered by a topclad layer on its top and both sides, and sit on a bottom clad layer,wherein an external electromagnetic wave is divided to a TE and TMelectromagnetic wave based on the thicknesses of the waveguide and thetop clad layer.

From the above descriptions, the present invention also discloses amethod for manufacturing an optic component, including the followingsteps: (1) a bottom clad layer on a substrate is provided and (2) awaveguide is formed on the bottom clad layer and surrounded by a topclad layer on its top and both sides, wherein the optic component isdesigned according to a pattern, an external electromagnetic wave isdivided to a TE and TM electromagnetic wave based on the thickness ofthe waveguide and the top clad layer.

The above aspects and advantages of the present invention will becomemore readily apparent to those ordinarily skilled in the art afterreviewing the following detailed descriptions and accompanying drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows that the provided optical chip, basically formed by thepolarization diversity coupler 101, the two-step taper waveguide 102,the multi-mode interferometer (MMI, 103) splitter, the bendingwaveguides 104, and the phase modulators (1051, 1052), is integratedinto a silicon-based MIOC 100, and the illustration (106, 107) shows thetop view of the polarization diversity coupler 101;

FIG. 2 a shows that the FOG configuration integrated with the disclosedsilicon-based MIOC;

FIG. 2 b shows that the functional layout schematics of thesilicon-based MIOC with its two outputs connected to a fiber sensingcoil;

FIG. 3 a shows that a 3D perspective drawing of the polarizationdiversity coupler 300 which is designed based upon the asymmetry inindex of optical refraction;

FIG. 3 b shows that a cross-section of the polarization diversitycoupler 300 along the aa′ dash-line of FIG. 3 a;

FIG. 3 c shows that the FimmWave simulation is used to discover therelation between the width and the effective refractive index of the Siwaveguide;

FIG. 3 d shows that the FimmWave simulation is used to discover therelation between the thickness of the SiC guiding layer (top clad layer)and the intensities of TE and TM waves;

FIG. 3 e shows the cross-section (as revealed in FIG. 3 b) distributionof the optical field of TE and TM waves along their propagatingdirection (FIG. 3 a, left to right);

FIG. 4 shows a schematic diagram of the two-step taper waveguide 400 inthe present invention;

FIG. 5 shows a schematic diagram of a multi-mode interferometer (MMI)splitter 500 introduced for performing light combing and splitting;

FIG. 6 shows a schematic diagram of a bending waveguide 600 includingtwo bending radius 601, 602, and a phase modulator 603;

FIG. 7 shows a schematic profile of the phase modulator 700; and

FIG. 8, including 8(a) to 8(f) show the manufacturing processes of thedisclosed Si-based MIOC.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more specifically withreference to the following embodiments. It is to be noted that thefollowing descriptions of preferred embodiments of this invention arepresented herein for the purposes of illustration and description only.It is not intended to be exhaustive or to be limited to the precise formdisclosed.

With the present invention, the provided silicon-based MIOC 100 whichcan be integrated into FOGs and other fiber sensors is basically formedby the polarization diversity coupler 101, the two-step taper waveguide102, the multi-mode interferometer (MMI) splitter 103, and the phasemodulator 1051 and 1052, as shown in FIG. 1. The following sectionsdescribe the provided optic chip in detail.

Please refer to FIG. 2 a, which is the FOG configuration integrated withthe disclosed silicon-based MIOC. Light is coupled into the fibersensing loop from a broadband light source via a circulator first, thendivided into clockwise and counterclockwise light through the disclosedsilicon-based MIOC. Based on the Sagnac effect, the return signalshaving optical path difference between the two propagating waves due torotation rate interfered and detected by the photodetector. To suppressthe polarization cross-coupling error and maintain reciprocity for thetwo counter-propagating waves, single-mode, single polarizationoperation is needed. In addition, phase modulation to the twopropagating waves is needed to resolve the rotation polarity, increasethe detection sensitivity, and widen the rate input dynamic range.

Please refer to FIG. 2 b, which is the system schematics ofsilicon-based MIOC 200 applied to the optical gyro. The polarizationdiversity coupler 201 divides an external light into TE and TM waves, inwhich the TE wave is coupled into the Si waveguide 202 and the TM waveis output along the SiC waveguide 203. The TE wave is transported by theSi waveguide 202, and is then divided into two equal optical signals byY-junction 204. After that, the divided TE waves will be respectivelyinput to the fiber loop 207 through the two different routes for thefurther treatment, wherein one of the two routes includes the phasemodulator 2051 and the polarization diversity coupler 2061 and the otherincludes the phase modulator 2052 and the polarization diversity coupler2062.

Please refer to FIG. 3 a, which is a 3D perspective drawing of thepolarization diversity coupler 300 designed based upon the asymmetry inindex of optical refraction. The polarization diversity coupler 300, asdescribed in FIG. 3 a, consists of a silicon carbide (SiC) guiding layer301 (top clad layer) with the thickness A₁=2.5 μm, the width B₁=3 μm andthe length (C₁+C₂)=(25+78) μm, wherein C₂ (78 μm) is the length of theSi waveguide 302 and C₁ (25 μm) is the distance between the tip of theSi waveguide 302 and the side of the SiC top clad layer 301, and asilicon (Si) waveguide 302 having the thickness A₂=0.13 μm, the tipwidth B₂=0.4 μm and the wider width B₃=1.0 μm which is partly inside andpartly outside the SiC top clad layer 301, wherein the outside part hasan length C₃=25 μm. The thickness of Si waveguide 302 is designed toallow only one TE guided mode confined in the Si waveguide while rejectall the TM guided modes.

Please refer to FIG. 3 b, which is a cross-section of the polarizationdiversity coupler 300 along the aa′ dash-line of FIG. 3 a. The Siwaveguide 302 is covered by the SiC top clad layer 301, and sit on thesilicon dioxide (SiO₂) bottom clad layer 303, wherein the thickness A₁of the SiC top clad layer is 2.5 μm, and the thickness A₂ of the Siwaveguide 302 is 0.13 μm.

Four unique features are conceived and employed to design thepolarization diversity coupler 300: (1) The thickness A₂ of the Siwaveguide 302 is determined by the cutoff condition. The cutoffcondition is the maximum thickness which is allowing TE but rejecting TMwaves to pass through the Si waveguide. We can separate the TE and TMwaves by controlling the thickness A₂ of Si waveguide. We calculate thethickness A₂ of the Si waveguide 302 for guiding TE wave is between 79and 150 nm, based on the waveguide theory. In the embodiment, thethickness A₂ is set to be 130 nm for the tolerance of fabrication error.(2) The TE wave is to be coupled into the Si waveguide 302, when thephase matching condition is achieved. This means that the effectiverefractive index of the Si waveguide 302 varies with the width of Siwaveguide 302, so the launched TE wave is coupled into the Si waveguide302 once the effective refractive index of the Si waveguide 302 matchesto that of SiC guiding layer 301 (top clad layer). We use the FimmWavesimulation software to discover the relation between the width and theeffective refractive index of the Si waveguide 302, as shown in FIG. 3c. As you can see, the effective refractive index of the Si waveguide302 increases while the Si waveguide 302 widens, and is equal to that ofthe SiC guiding layer 301 (top clad layer) when the width of the Siwaveguide 302 is near 650 nm. The widths of Si waveguide 302 aredesigned to be 0.4 μm and 1 μm representing the beginning and the end ofthe Si waveguide 302 respectively, to make sure most of the TE wave canbe coupled to the Si waveguide 302 within a very short distance C₂=78μm. (3) The TE and TM polarization extinction ratio is determined by thesize of the SiC guiding layer 301 (top clad layer). We again use theFimmWave simulation software to discover the relation between thethickness of the SiC guiding layer 301 (top clad layer) and thecross-section field distribution of TE and TM waves inside the Si andSiC waveguides, as shown in FIG. 3 d. As you can see from the dashedline frame 304, the thickness of the SiC guiding layer 301 (top cladlayer) must be greater than 2.5 μm, or else the part of TM wave willleak into the Si waveguide 302, wherein the dash-line frames 3041 and3042 represent the cross-section field distribution at the beginning andthe end of the Si waveguide 302 in FIG. 3 a, respectively. FIG. 3 esummarizes the above description, and reveals the most important featureof the polarization diversity coupler on how TE and TM waves propagatingin Si and SiC waveguides respectively. The top view on the right handside shows a Si taper waveguide. And a rectangular SiC guiding layer(top clad layer) on top of Si waveguide. Within only 78 μm, TE and TMwaves are completely separated. (4) In the embodiment, in order toobtain the larger extinction ratio, a 90 degree bend is made in the SiCguiding layer (203 in FIG. 2 b) with respect to the direction of the Siwaveguide (202 in FIG. 2 b) to divert the TM wave to the chip edge. As aresult, the extinction ratio of the present optic chip with thepolarization diversity coupler 300 can be deduced to 30 dB.

Please refer to FIG. 4, which shows a schematic diagram of the two-steptaper waveguide 400 in the present invention. The two-step taperwaveguide 400 is used to bridge the Si waveguide 302 in the polarizationdiversity coupler 300 (referring to FIG. 3 a) and a multi-modeinterferometer (MMI) splitter (referring to FIG. 5 of the followingparagraph). Preferably, in order to reduce an optical loss and realize asingle-mode propagation of the TE wave, the thickness in 401 waveguidesection and the width in 403 waveguide section of the two-step taperwaveguide 400 need to be increased and decreased, respectively. As aresult, a vertical and lateral taper are required and manufactured inthe two-step taper waveguide 400. Preferably, the two-step taperwaveguide 400 is made of silicon. Based on the above-mentioned and theBMP (Beam Propagation Method) and the FimmProp simulation, we designed avertical taper 401 with L₁=2.0 μm in length, W₁=1.0 μm, and a heightincreases from H₁=0.13 μm to H₂=0.22 μm, followed by the samecross-section waveguide 402 having the length L₂=25 μm, the width W₂=1.0μm and the height H₂=0.22 μm, and a lateral taper 403 for single-modeoperation having L₃=20 μm in length and a width decreases from W₂=1.0 μmto W₃=0.6 μm.

Please refer to FIG. 5, which is a schematic diagram of a multi-modeinterferometer (MMI) splitter 500 introduced for performing lightcombing and splitting. Preferably, an input light is split to two lightsdue to the designed length of the MMI 500. Preferably, in order toreduce an optical reflection and coupling loss, one taper waveguide 501and two taper waveguides (502, 503) are designed and installed at theinput and output end of the MMI 500, respectively. Preferably, the MMI500 is an one-by-two multimode interference splitters. After a TE waveform the two-step taper waveguide 400 (referring to FIG. 4) emits to theMMI 500, it is split into two TE waves with a 50/50 splitting ratio. Inthe embodiment, the length and width of the MMI 500, not including 501,502, and 503, is set as 75 and 9 μm, respectively. Preferably, thesplitting loss is less than 0.9 dB based on the result of BMPsimulation.

Please refer to FIG. 6, which is a schematic diagram of a bendingwaveguide 600 including the phase modulator 603 corresponding to thephase modulators 1051, 1052 of FIG. 1. In order to reduce the couplingloss, two bending waveguides are introduced to connect with the twooutput taper waveguides 502, 503 for bridging the MMI 500 (referring toFIG. 5) and the phase modulator. Preferably, the bending waveguide 600is the Si waveguide with a double bending structure which means that thebending waveguide 600 has an inner 601(r ₁) and an outer 602(r ₂)radiuses of curvature. In the embodiment, an inner 601 and an outer 602radiuses of curvature are 149.7 μm and 150.3 μm, respectively. Becausethe radiuses of curvature are big enough and the confinement effect ofthe Si waveguide is strong, the bending loss will be small when the TEwave propagates in the bending waveguide 600.

Please refer to FIG. 7, which is a schematic profile of the phasemodulator 700. The structure of the phase modulator 700 is a ridwaveguide 701, and the phase modulator 700 is connected with the bendingwaveguide 600 (referring to FIG. 6). Therein, the phase modulation isaccomplished via the dispersion effect of the free carriers. This meansthat by controlling the concentration of free carriers in the ridwaveguide 701, the phase modulation can be performed. As shown in FIG.7, the boron (B) ions are doped into the portion on one side of the ridwaveguide 701 to form the P-type doping region 702 and the nitrenium (N)ions are doped into the portion on another side of the rid waveguide 701to form the N-type doping region 703. The refractive index of the ridwaveguide 701 can be changed by applying the bias voltage 704 to changethe electron hole density in the rid waveguide 701. In theimplementation, the rid waveguides 701 is the Si waveguide and itslength is 109 μm. The π phase offset can be achieved by applying bias of1.5 V and the frequency modulation of 20 MHz. In one measurement, the 3dB bandwidth of the phase modulators was greater than 80 MHz which canbe further improved through design and process improvement.

Please refer to FIG. 8, which is a flow chart of the manufacturingprocess of the present application. The P-type SOI(silicon-on-insulator) wafer is used to manufacture the optical chip 100(referring to FIG. 1). There are 6 photomaskes, (1) Si mask 801, (2)Waveguide mask 802, (3) P-type doping mask 803P, (4) N-type doping mask803N, (5) SiC upper clad layer mask 804 and (6) Al metal layer mask 805,have been introduced during the process. For the pretreatment, thethermal oxidation by a Horizontal Furnace and the etching by buffedoxide etch (BOE) are performed in order to thin the thickness of the Silayer of the P-type SOI wafer from 250 μm to 220 μm. The manufacturingprocess of the present application includes the following steps:

Step 801: Referring to FIG. 8 a, it shows the manufacturing steps of Sipatterns including the two-step taper transitions. First, the siliconnitride is deposited on the wafer by a furnace as a 100 nm barrier layer8011. Then, the photoresist is spin-coated onto the silicon nitridelayer. After carrying out the soft baking and the hard baking process,an exposure then is performed by irradiating a light beam through thefirst photomask (801 in FIG. 8). The photoresist layer then is developedto form a first photoresist pattern on the wafer. The above processesare called the photolithography 8012. Then, the sample is etched byreactive-ion-etch (RIE) for 10 seconds to remove the silicon nitrideundefined by the first photomask (i.e., the unwanted portion of thefirst pattern). After that, the dry photoresist stripper (Mattson ASPENAsher) and SPM (H₂SO₄) are used to remove the remaining photoresist8013. Finally, the TCP-9400 Poly Si Etcher is used to remove 90 nm of Sifrom the surface. Due to the high etching selectivity between siliconnitride and Si, we can measure the thickness of the surface etch bySurface Profiler.

Step 802: Referring to FIG. 8 b, it shows the manufacturing steps ofwaveguides including a multi-mode interferometer (MMI) splitter and ridwaveguides, wherein the rid waveguide has ability for single-modepropagation. In this step, the patterns of all rid waveguides aredefined by the second photomask and formed by the photolithography 8021.As a result, the pattern of the second photomask (Waveguide mask) willbe developed on the SOI wafer. Then, 8022 the TCP-9400 Poly Si Etcher isused to remove 90 nm of Si from the surface. Finally, 8023 the dryphotoresist stripper (Mattson ASPEN Asher) and SPM (H₂SO₄) are used toremove the remaining photoresist.

Step 803P: To form the phase modulator having two different type dopingregions, two steps are included. For Step 803 a: Referring to FIG. 8 c,it shows the manufacturing steps of the P-type doping region. The P-typedoping region is designed and formed by the photolithography process803P1. As a result, the pattern of the third photomask (P-type dopingmask) will be formed on the SOI wafer. Then, 803P2 the medium currention implanter (Implantation E500HP) is used to implant the boron (B)ions to form 803P4 the P-type doping region. Finally, 803P3 the dryphotoresist stripper (Mattson ASPEN Asher) and SPM (H₂SO₄) are used toremove the remaining photoresist.

For Step 803N: Referring to FIG. 8 d, it shows the manufacturing stepsof the N-type doping region. The N-type doping region is designed andformed by the photolithography process 803N1. As a result, the patternof the fourth photomask (N-type doping mask) will be formed on the SOIwafer. Then, 803N2 the medium current ion implanter (ImplantationE500HP) is used to implant the phosphorus (P) ions to form 803N4 theN-type doping region. Finally, 803N3 the dry photoresist stripper(Mattson ASPEN Asher) and SPM (H₂SO₄) are used to remove the remainingphotoresist.

Step 804: Referring to FIG. 8 e, it shows the manufacturing steps of theSiC waveguide, the upper clad layer of the Si waveguide, for guiding theunwanted TM wave in the Polarization Diversity Coupler to the chip sideedge. For the pretreatment 8041, the silicon dioxide is deposited on thesample by a furnace as a 3 μm barrier layer. Then 8042, the photoresistis spin-coated onto the silicon dioxide layer. After carrying out thesoft baking and the hard baking process, an exposure then is performedin the I-line stepper by irradiating a light beam through the fifthphotomask (SiC mask). The photoresist layer then is developed in theTrack to form a fifth photoresist pattern on the wafer. Then, 8043 thephotoresist is spin-coated onto the backside of the SOI wafer. Aftercarrying out the soft baking and the hard baking process again, thesample is wet-etched 8044 by BOE for 340 seconds to remove the silicondioxide undefined by the fifth photomask (i.e., the unwanted portion ofthe fifth pattern). Because the anisotropic etching characteristic ofthe wet-etch, the bowl space will be formed in the silicon dioxidelayer. While the over etching happens, the photoresist is removed by thedry photoresist stripper (Mattson ASPEN Asher) and SPM (H₂SO₄). Then,8045 the 7 μm SiC is deposited on the sample by the plasma-enhancedchemical vapor deposition (PECVD). After that, 8046 the SiC is thinneddown by the chemical mechanical polishing (CMP) until the designed layerthickness remains.

Step 805: Referring to FIG. 8 f, it shows the manufacturing steps ofevaporating a metal layer on the sample for phase modulators connection.The pattern of the metal layer is designed and formed on the sample bythe photolithography process 8051. As a result, the pattern of the sixthphotomask (Al mask) will be formed on the wafer. Then, 8052 the 5000 ÅAl layer is deposited on the sample by the electron beam gun (E-gun).Finally, 8053 the lift-off process is carried out by the acetone andSPM-2 (H₂SO₄) to remove the remaining photoresist and the metal layer.

Based on the above steps, the optical chip which can be integrated intothe gyros is completed.

There are still other embodiments, which are described as follows.

Embodiment could be:

1. An optic chip, comprising: a polarization diversity coupler having awaveguide with a first thickness and a width, and a top clad layer witha second thickness which surrounds the top and both sides of waveguide,and generating a TE electromagnetic wave and a TM electromagnetic waveaccording to an inputted external electromagnetic wave based on thefirst thickness and the second thickness, wherein one of the TEelectromagnetic wave and the TM electromagnetic wave is coupled into thewaveguide based on the width of waveguide and the thicknesses ofwaveguide and top clad layer.

2. An optic chip as claimed in Embodiment 1 further comprising a bottomclad layer, wherein the waveguide, the top clad layer, and the bottomclad layer have a first, a second and a third refractive indexrespectively, the first refractive index is bigger than the secondrefractive index, and the second refractive index is bigger than thethird refractive index.

3. An optic chip as claimed in Embodiment 2, wherein the waveguide is aguiding layer made from the silicon, the top clad layer is the siliconcarbide (SiC), and the bottom clad layer is the silicon dioxide.

4. An optic chip as claimed in Embodiment 1, wherein the waveguide is ataper waveguide.

5. An optic chip as claimed in Embodiment 4, wherein the taper waveguidecan guide one of the TE and TM electromagnetic waves to the output sideof the polarization diversity coupler.

6. An optic chip as claimed in Embodiment 1, wherein the thicknesses ofthe waveguide and the top clad layer are obtained by FimmWave simulationor BPM simulation or the other simulation softwares.

7. An optic chip as claimed in Embodiment 1, wherein the top clad layerturns out the optic chip in 90 degree or any other bending angleadequate to reach the edge of the optic chip for outputting the unwantedpolarized electromagnetic waves from the polarization diversity coupler.

8. An optic chip as claimed in Embodiment 7, wherein the structure ofthe clad layers further increases an extinction ratio in the optic chipby preventing the unwanted polarized electromagnetic waves formreflecting back to the polarization diversity coupler.

9. An optic chip as claimed in Embodiment 1 further comprising amulti-mode interferometer (MMI) splitter, and a two-step taper waveguidebridging the waveguide and the MMI.

10. An optic chip as claimed in Embodiment 9, the two-step taperwaveguide comprises a vertical taper waveguide and a lateral taperwaveguide for reducing an optical loss and realizing single-modepropagation respectively.

11. An optic chip as claimed in Embodiment 9, wherein the two-step taperwaveguide is connected with part of the end of the polarizationdiversity coupler output for receiving the polarized electromagneticwave from the waveguide.

12. An optic chip as claimed in Embodiment 9, wherein the MMI has afirst plurality of waveguides at the input end and a second plurality ofwaveguides at the output end, and the first and second plurality ofwaveguides are taper waveguides which reduce the coupling loss.

13. An optic chip as claimed in Embodiment 12, wherein a plurality ofbending waveguides is connected with the second plurality of waveguidesto increase separation between the two output waveguides for ease offiber pigtailings at the chip edge.

14. An optic chip as claimed in Embodiment 9, wherein the two-step taperwaveguide, the multi-mode interferometer (MMI) splitter and theplurality of bending waveguide are made from the silicon.

15. An optic chip as claimed in Embodiment 14, wherein the plurality ofbending waveguides prevents the two output waveguides from coupling toeach other.

16. An optic chip as claimed in Embodiment 15, wherein the plurality ofbending waveguides is a plurality of rid waveguides.

17. An optic chip as claimed in Embodiment 9, wherein the MMI is anone-by-two multimode interference splitters to divide the polarizedelectromagnetic wave from the waveguide into a 50/50 splitting ratiooutput to form a Y-junction.

18. An optic chip as claimed in Embodiment 17, wherein the Y-junctionincludes two optical branches for propagating the polarizedelectromagnetic wave.

19. An optic chip as claimed in Embodiment 17, wherein a phase modulatoris connected at one side or both sides of the Y-junction output arms toachieve an optical phase modulation.

20. An optic chip as claimed in Embodiment 19, wherein two polarizationdiversity couplers are connected with two ends of the phase modulator.

21. An optic chip as claimed in Embodiment 19, wherein the optical phasemodulation is achieved through one of the following physics mechanisms:a plasma dispersion, an electro-optics, a thermo-optics and aphoto-elastic effect.

22. A method for manufacturing an optic chip, comprising: (a) asubstrate is provided; (b) forming a two-step taper waveguide on thesubstrate; and (c) connecting a multi-mode interferometer (MMI) splitterwith the two-step taper waveguide, wherein the MMI splitter having anoutput end comprising at least one taper waveguide or an output endcomprising at least two taper waveguides for a single-mode propagationand (d) forming a polarization diversity coupler connected with thetwo-step taper waveguide, for splitting an electromagnetic wave, havinga waveguide with a width and a first thickness, and a top clad layerwith a second thickness.

23. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the electromagnetic wave is split into a TE electromagneticwave and a TM electromagnetic wave based on the first thickness of thewaveguide and the second thickness of the top clad layer, and one of theTE electromagnetic wave and the TM electromagnetic wave is coupled intothe waveguide based on the width of the waveguide, and the thicknessesof waveguide and the top clad layer.

24. A method for manufacturing an optic chip as claimed in Embodiment22, wherein a refractive index of the waveguide is bigger than arefractive index of the top clad layer, and the refractive index of thetop clad layer is bigger than a refractive index of the bottom cladlayer.

25. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the waveguide is a taper waveguide.

26. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the taper waveguide can guide one of the TE and TMelectromagnetic waves to the output side of the polarization diversitycoupler.

27. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the substrate and the bottom clad layer is a SOI wafer.

28. A method for manufacturing an optic chip as claimed in Embodiment22, further comprising in the step (a): (a1) the substrate is treated bya thermal oxide in a furnace; and (a2) a silicon thickness of the SOIwafer is reduced by a wet-etch process using BOE.

29. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the polarization diversity coupler includes a siliconcarbide (SiC) guiding layer as the top clad layer, a silicon (Si)guiding layer as the waveguide and the SiO₂ insulator as the bottom cladlayer.

30. A method for manufacturing an optic chip as claimed in Embodiment22, wherein which one of the TE and TM electromagnetic waves beingcoupled into the waveguide is determined by the width of the waveguideand the thicknesses of waveguide and top clad layer.

31. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the thicknesses of the waveguide and the top clad layer areobtained by FimmWave simulation or BPM simulation or the othersimulation softwares.

32. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the top clad layer turns out the optic chip in 90 degree orany other bending angle adequate to reach the edge of the optic chip foroutputting the unwanted polarized electromagnetic waves from thepolarization diversity coupler.

33. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the structure of the top clad layer further increases anextinction ratio in the optic chip by preventing the unwanted polarizedelectromagnetic waves form reflecting back to the polarization diversitycoupler.

34. A method for manufacturing an optic chip as claimed in Embodiment22, further comprising in the step (b): (b1) a first photolithographyprocess is performed to form the first pattern, wherein a firstphotomask is used in the first photolithography process; (b2) a firstetching process is performed to reduce the thickness of the waveguidelayer to reach a designed first thickness, wherein the first etchingprocess is a dry etching process; and (b3) a first photoresist stripprocess is performed to remove the remained photoresist in step (b1) bya dry photoresist stripper and a H₂SO₄ solution (SPM).

35. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the two-step taper waveguide is connected with part of theend of the polarization diversity coupler output for receiving thepolarized electromagnetic wave from the waveguide.

36. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the two-step taper waveguide is a vertical and lateral taperwaveguide for reducing an optical loss and realizing a single-modepropagation respectively.

38. A method for manufacturing an optic chip as claimed in Embodiment22, further comprising in the step (c): (c1) a second photolithographyprocess is performed to form the second pattern after depositing asilicon nitride on the substrate as a barrier layer, wherein a secondphotomask is used in the second photolithography process; (c2) theportion of the silicon nitride area undefined by the second photomask isremoved by a reactive ion etch (RIE); (c3) a second photoresist stripprocess is performed to remove the remained photoresist in step (c1) bya dry photoresist stripper and a H₂SO₄ solution (SPM); and (c4) a secondetching process is performed to reduce the thickness of the waveguidelayer to reach a designed second thickness, wherein the second etchingprocess is a dry etching process.

39. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the MMI is an one-by-two multimode interference to dividethe polarized electromagnetic wave from the waveguide into a 50/50splitting ratio output to form a Y-junction.

40. A method for manufacturing an optic chip as claimed in Embodiment39, wherein the Y-junction includes two optical branches for propagatingthe polarized electromagnetic wave.

41. A method for manufacturing an optic chip as claimed in Embodiment40, wherein a phase modulator is connected at one side or both sides ofthe Y-junction output arms to achieve an optical phase modulation.

42. A method for manufacturing an optic chip as claimed in Embodiment41, wherein the optical phase modulation is achieved through one of thefollowing physics mechanisms: a plasma dispersion, an electro-optics, athermo-optics and a photo-elastic effect.

43. A method for manufacturing an optic chip as claimed in Embodiment42, wherein the plurality of bending waveguides are a plurality of ridwaveguides.

44. A method for manufacturing an optic chip as claimed in Embodiment43, wherein the two bending waveguides are manufactured in the step (c)of Embodiment 22.

45. A method for manufacturing an optic chip as claimed in Embodiment22, wherein a plurality of bending waveguides are connected with theplurality of waveguides at the output end of the MMI.

46. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the plurality of waveguides including a first and a secondwaveguides at the output and a third waveguide at the input end of theMMI are taper waveguides which reduce an optical reflection and couplingloss.

47. A method for manufacturing an optic chip as claimed in Embodiment46, wherein the first and second bending waveguides prevent the twooutput waveguides from coupling to each other.

48. A method for manufacturing an optic chip as claimed in Embodiment22, wherein the two-step taper waveguide, the multi-mode interferometer(MMI) splitter and the plurality of bending waveguide are made from thesilicon.

49. A method for manufacturing an optic chip as claimed in Embodiment22, further comprising in the step (d): (d1) a third photolithographyprocess is performed to form the third pattern after a silicon nitrideis deposited on the substrate as a barrier layer, wherein a thirdphotomask for designing a silicon carbide (SiC) waveguide is used in thethird photolithography process; (d2) a third etching process using BOEis performed to remove the portion of the SiO₂ layer undefined by thethird photomask, wherein the removed portion of the SiO₂ layer is a bowlspace; (d3) a third photoresist strip process is performed to remove theremained photoresist in step (d1) by a dry photoresist stripper and aH₂SO₄ solution (SPM); (d4) the SiC is deposited on the waveguidesubstrate by a plasma-enhanced chemical vapor deposition (PECVD); and(d5) a polish process is performed to removed the SiC outside the bowlspace.

50. A method for manufacturing an optic chip as claimed in Embodiment22, after step (c), further comprising the steps: (I) a phase modulatoris formed on the waveguide substrate for a light modulation, wherein thephase modulator includes a P-type doping and N-type doping region.

51. A method for manufacturing an optic chip as claimed in Embodiment50, wherein the phase modulation is performed by free carriers.

52. A method for manufacturing an optic chip as claimed in Embodiment50, further comprising in the step (I): (Ia) a forth photolithographyprocess is performed to form a forth pattern, wherein the forth patternis designed for P-type doping, and then a photoresist is removed; and(Ib) a fifth photolithography process is performed to form a fifthpattern, wherein the fifth pattern is designed for N-type doping, andthen a photoresist is removed.

53. A method for manufacturing an optic chip as claimed in Embodiment50, wherein a plurality of boron (B) ions and a plurality of nitrenium(N) ions are respectively used to form the P-type doping region and theN-type doping region by a doping process.

54. A method for manufacturing an optic chip as claimed in Embodiment 23and Embodiment 24, after the step (4), further comprising: (IIa) a sixthphotolithography process is performed to form the sixth pattern; (IIb) aforth etching process using BOE is performed to remove the portion ofthe SiO₂ layer undefined by the sixth photomask, wherein the removedportion of the SiO₂ layer is a bowl space; (IIc) an evaporation coateris used to evaporate a metal on the substrate to form a metal layer,wherein some of the metal layer is coated on the bottom of the bowlspace and the others is coated on the photoresist; and (IId) a lift-offprocess is performed to remove the photoresist, wherein the metal layercoated on the photoresist is removed along with the photoresist and themetal layer coated on the bottom of the bowl space is remained.

55. A method for manufacturing an optic chip as claimed in Embodiment54, wherein the evaporation coater is an electron gun system, the metalis an aluminum (Al) and an acetone and a H₂SO₄ solution (SPM) are usedin the lift-off process.

56. A method for manufacturing an optic chip as claimed in Embodiment54, wherein the metal layer coated on the bottom of the bowl space isused to conduct the electrons from the N-type doping region and theelectron holes from the P-type doping region in order to control theconcentration of free carriers in the Si waveguides.

In conclusion, by means of the designed polarization diversity couplerof the optical chip, the external light will be coupled into thewaveguide within a very short distance and be split into TE and TMwaves. In the optical chip of the present invention, in addition to thesingle-mode operation, the great extinction ratio is obtained by addingthe bending waveguides to the polarization diversity coupler output.Also, a unique two-step (vertical and lateral) taper waveguide region isdesigned and fabricated to bridge the polarization-diversity coupleroutput with the input of a multi-mode interferometer (MMI) splitter forpower loss reduction. The MMI is to divide the input polarized lightinto a 50/50 splitting ratio output to form a Y-junction for interfacingsplitted light beams with an external sensing element such as a fibersensing coil for FOG applications. Based on the above description, it isclear that applicants had conceived and implemented a practicalsilicon-based MIOC to integrate functions of Y-junction splitter,polarizer, and phase modulators on the single optical chip through theimplementation of a unique polarization diversity coupler, and thetwo-step taper waveguide designs for single-mode, single polarization,and low loss sensor applications. Such integration has additionaladvantages in reducing packaging and alignment cost for discretecomponents, and above all, Si-based MIOC is relatively small in size andis compatible with CMOS IC processes. It is feasible to foresee theintegration of MIOC with the sensor electronics in one single unit.

Based on the above descriptions, it is understood that the presentinvention is indeed an industrially applicable, novel and obvious onewith values in industrial development. While the invention has beendescribed in terms of what are presently considered to be the mostpractical and preferred embodiments, it is to be understood that theinvention should not be limited to the disclosed embodiment. On thecontrary, it is intended to cover numerous modifications and variationsincluded within the spirit and scope of the appended claims which are tobe accorded with the broadest interpretation so as to encompass all suchmodifications and variations. Therefore, the above description andillustration should not be taken as limiting the scope of the presentinvention which is defined by the appended claims.

What is claimed is:
 1. An optic component, comprising: a waveguidehaving a width and coupling a polarized light based on the width; and aset of asymmetric waveguide refractive indices on which the polarizedlight being one of a TE light and a TM light and generated by dividingan inputted light is based on the optic component structure.
 2. An opticcomponent as claimed in claim 1 further comprising a top and a bottomclad layers, wherein the waveguide, the top clad layer, and the bottomclay layer have a first, a second and a third refractive indexrespectively, the first refractive index is bigger than the secondrefractive index, and the second refractive index is bigger than thethird refractive index.
 3. An optic component as claimed in claim 1further comprising an edge, wherein the top clad layer bends to an angleadequate to reach the edge for outputting the unwanted polarizedelectromagnetic waves.
 4. An optic component as claimed in claim 1,wherein the waveguide is a taper waveguide.
 5. A method of manufacturingan optic component, comprising: forming a waveguide having a width; andproviding a set of asymmetric waveguide refractive indices, wherein thewaveguide couples a polarized light based on the width of the waveguide,and the polarized light is one of a TE light and a TM light generated bydividing an inputted light based on the set of asymmetric waveguiderefractive indices.
 6. A method of manufacturing an optic component asclaimed in claim 5 further comprising steps of: providing a bottom cladlayer on a substrate on which the waveguide is disposed; and coveringthe waveguide by a top clad layer.
 7. A method of manufacturing an opticcomponent as claimed in claim 6, wherein a refractive index of thewaveguide is bigger than a refractive index of the top clad layer, andthe refractive index of the top clad layer is bigger than a refractiveindex of the bottom clad layer.
 8. A method of manufacturing an opticcomponent as claimed in claim 6, wherein the top clad layer bends to anangle adequate to reach an edge of the optic component for outputtingthe unwanted polarized electromagnetic waves.
 9. A method ofmanufacturing an optic component as claimed in claim 6, wherein thewaveguide is a taper waveguide.